1. Field of the Invention
The present invention relates to tape cassettes in general.
2. Description of the Prior Art
Prior art techniques have provided tape cassettes equipped with an accidental erasure preventive slot on the bottom side thereof which is normally covered with a blocking element. With the blocking element removed, the slot causes a detector of the associated tape recorder to operate, thus making the recording button inoperative. In other words, a tape cassette with its blocking element removed, after recording, inhibits duplicate recording, i.e., erasing. This, however, gives rise to the problem that the slot must be filled with something to function as the blocking element, or the cassette itself must be replaced with a new one, when the tape is to be used again for re-recording thereon, or where it is run for erasing and re-recording.
One prior art solution to this problem is an arrangement which permits the blocking element to be slid or turned over on a hinge. This again is impractical for chrome-bias tape cassettes or like cassettes in which the bias changeover slot is formed adjacent to the accidental erasure preventive slot, because the blocking element readily closes the bias changeover slot when it is slid or turned over.
These prior art approaches will be described in more detail by referring to the appended drawing, wherein, for example, FIGS. 1 and 2 schematically show the construction of one popularly known tape cassette with a bias changeover slot 3, in which a blocking element 1 is disposed thereon for covering the opening of an accidental erasure preventive slot 2 located adjacent to the bias changeover slot 3. The blocking element 1 is necessary for recording, but must be removed by detaching it from its base 4 when the recorded data is to be prevented from being erased by mistake. Without the blocking element 1, the accidental erasure preventive slot 2 is open to a detection rod extended from the accidental erasure preventive device, e.g., a microswitch, installed in the associated tape recorder. When the detection rod enters the slot 2, the microswitch operates to make the recording button of the recorder inoperative. Hence, on a tape cassette, with its blocking element removed, erasing is not effected, but only playback is available.
When a tape recorder provided with an automatic chrome-bias changeover mechanism is used, the bias changeover slot is open to the bias changeover mechanism of the recorder, permitting chrome-bias recording to start automatically. As described above, tape cassettes of the type having no bias changeover slot involve difficulties once the blocking element is detached. Prior art techniques have proposed the following improvements on this type of tape cassette. With reference to FIG. 3, for example, where a schematic plan view is shown to illustrate part of such a tape cassette, in which a plastic plate 5 is used instead of the usual blocking element, the plate 5 is moved in the direction indicated by an arrow 6, i.e., toward the center of the cassette, after recording, whereby the accidental erasure preventive slot is opened.
Another prior art improvement is schematically shown in FIGS. 4 and 5, in which a plastic plate 7, swingable on a hinge 8, is used instead of the usual blocking element. The hinge 8 is held in a column 9 formed within a case body 11. An accidental erasure preventive slot 12 can be opened by pivoting the plate 7 in the direction of an arrow 10, i.e., toward the center of the case 11. The plate 7 is thus turned over and fitted to the case 11.
These prior art arrangements cannot be utilized for tape cassettes of the type equipped with a bias changeover slot because the plate 5 or 7 necessarily covers the bias changeover slot when it is slid or turned over to open the accidental erasure preventive slot.
Another prior art solution to the problem is the use of a plug instead of the usual blocking element, which can be pulled out to open the slot and set into position to close it when necessary, as in digital tape cassettes. This construction, however, poses another problem, in that the plug is very likely to be lost once it is removed.